Workstation Design The Art & Science of Fitting the Work to the Person Learning Outcomes After careful studying this chapter You should be able to: Discuss the disadvantages of static loads, Explain the causes of fall and how to prevent them, Describe solutions to reduce Musculoskeletal Disorders, Define the optimal work height and how to fit different persons to work height, Discuss the benefits of ergonomic work stations, Understand when to use the hands, the arms, the legs, Explain the characteristic of using the preferred hand, Alternatives for Including as Many People as Possible 1
Ergonomic Design Considerations Product/equipment Job aids User selection (Note: and then Job Modification) Training of user Guideline 1: Avoid Static Loads and Fixed Work Postures Static load increases systolic and diastolic blood pressure. Metabolic wastes accumulate in the muscles. Consider increasing recovery time. 2
Standing Shoes affect center of gravity and forward bending moment. Have hips parallel to the floor. Provide bar rail to vary work posture. Hard floors cause standing fatigue and increase heart rate. Falls Slips and falls are a major cause of unintentional injury deaths and have an annual direct cost/capita of $50 to 400. Causes of falls: Slips: Unexpected horizontal foot movement Trips: Restriction of foot movement Stepping-on-air: Unexpected vertical foot movement 3
Solutions for Falls Prevent them: Use well-designed ladders, scaffolds, and ramps properly. Provide safe steps. Use the three-contact rule. Provide good friction and reduce lubricants. Reduce their consequences: Interrupt the fall. Soften the impact. Head Weight The head weighs about the same as a bowling ball. Keep the line of sight below the horizontal. Maintain forward head tilt of 10º 15º. Avoid backward and sideward tilts. 4
Hands/Arms An arm weighs about 4.4 kg. Avoid using the hand to hold up a tool or work piece. Avoid working with elevated hands. Support the arms on the work surface or chair arms. Consider using magnification. Source: Boeing Company, http://www.boeing.com/aboutus/environment/lead_ergo.htm 5
Guideline 2: Reduce Musculoskeletal Disorders Set the work height at 50 mm below the elbow. Don t bend your wrist. Don t lift your elbow. Don t reach behind your back. Follow guidelines for hand and arm motions. Source: Boeing Company, http://www.boeing.com/aboutus/environment/lead_ergo.htm 6
Guideline 3: Set the Work Height at 50 mm Below the Elbow Work height is defined in terms of elbow height. Optimum height is slightly below the elbow. Optimum height from the elbow is the same for sitting and standing. Work height is not table height. Solutions for Work Height Change machine height. Adjust elbow height. Adjust work height on machine. 7
Solutions for Work Height Office VDT Workstations Key items: screen, keyboard, document, eyes, hands Make sure workstation furniture is adjustable. Locate the primary visual element first: ahead of the eye, perpendicular to the line of sight. Train the operator in adjusting equipment. Provide a wrist rest. 8
Office VDT Workstations Laptop Computers and Mobile Devices Initially designed for short term use; now used frequently Issues stem from proximity of laptop (and similar mobile devices) monitor & keyboard to position the laptop monitor at the right height for your back and neck, you have to lift your arms and shoulders too high, causing shoulder and neck problems to position laptop keyboard at the best height for your arms and shoulders, you must hunch your shoulders and neck to see the monitor 9
Laptop Computers and Mobile Devices Laptop Computers and Mobile Devices Advice is similar to that of standard workstations Use a correctly set-up desktop computer instead of a laptop / mobile device as often as you can Use peripheral equipment, such as a docking station, separate keyboard, mouse and laptop stand Take frequent breaks Carry your laptop in a backpack or in wheel-along luggage ( TEXT - NECK!!!! 10
Guideline 4: Furnish Every Employee with an Adjustable Chair The cost of an adjustable chair is very low compared to labor cost. Allow users to try chairs in their specific jobs. Buy chairs that are easily adjustable. Train people in proper adjustment. Chair Design Seats Backrests Armrests Legs/bases 11
Guideline 5: Use the Feet as Well as the Hands The foot is slower and less dexterous than the hand. The legs can provide 3 times the power of the arms. Use pedals for power and control. Guideline 6: Use Gravity; Don t Oppose It Make movements horizontal or downward; avoid lifting. Consider using the weight of the body to increase mechanical force. Use gravity to move material to the work. Use gravity as a fixture. Use gravity in feeding and disposal. 12
Guideline 7: Conserve Momentum Avoid unnecessary acceleration and deceleration. Use circular motion for stirring and polishing. Follow through in disposal motions. Eliminate grasping motions by providing lips, rolled edges, and holes. Avoid transporting weight in the hand. Guideline 8: Use 2-Hand Motions Rather Than 1-Hand Motions Cranking with two arms is 25% more efficient than with one. Using two hands is more productive despite taking more time and effort. Don t use the hand as a fixture. 13
Guideline 9: Use Parallel Motions for Eye Control of 2- Hand Motions Minimize the degree of spread rather than worry about symmetry. Estimate the cost of eye control with predetermined time systems. Parallel vs. Symmetrical Motions BC DD B C C C A D B B A D A A Parallel motions Shoulder moves Easy eye travel Symmetrical motions Shoulder steady Difficult eye control 14
Guideline 10: Use Rowing Motions for 2-Hand Motions Alternation causes movement of the shoulder and twisting of the torso. Alternation causes higher heart rates. Rowing motions are more efficient and provide greater power. Guideline 11: Pivot Motions About the Elbow Motion time is minimized with motion about the elbow. Cross-body movements are more accurate than those about the elbow. Physiological cost is lower for movements about the elbow. 15
Guideline 12: Use the Preferred Hand The dominant hand is: 10% faster for reach-type motions More accurate than the non-dominant More exposed to cumulative trauma 5% to 10% stronger Work should arrive from the operator s preferred side and leave from the non-preferred side. Guideline 13: Keep Arm Motions in the Normal Work Area Avoid long work benches. Use swing-arms and lazy Susans. For high use, keep it close. It is easier to reach ahead of the shoulder than the nose. The shoulder is very sensitive to small changes in workplace layout. 16
Windshield Wiper Pattern Guideline 14: Let the Small Person Reach; Let the Large Person Fit Design a work station to allow most of the population to use it. Jobs must be designed for both male and female. Multi-person use of equipment and stations is more common. 17
Let the Small Person Reach; Let the Large Person Fit (cont.) When considering user populations, civilian industrial population data are not the same as military data. International populations may need to be considered. The percentage to exclude depends on the seriousness of designing people out and the cost of including more people. Alternatives for Including as Many People as Possible One size fits all Multiple sizes Adjustability 18
End of Chapter 19